Multiplex telephony.



} PATENTED MAR. 55, 1907. GOODRU'M. MULTIPLEX TELEPHONY. APPLICATION FILED MAR. 3, 1904.

J. W. LATTIG & G. L.

, UNITED STATES PATENT. OFFICE.

JACOB W. LATTIG, or WYNCOTE, AND CHARLES LANE coonnunor PHILADELPHIA, PENNSYLVANIA.

MULTIPLEX TELEPHONY.

Specification of Lette'i s Patent. Application filed March 3 1904. Serial No. 196,279.

Patented. March 5, 1907. v

United States, residing, respectively, in

Wyncote, Montgomery county, and in rhiladelphia, Philadelphia county, Pennsylvania, have invented certain new and useful Improvements in Multiplex Telephony, of which the following is a specification.

Our invention relates to means for transmitting more than one telephonic communication over the same Wires at the same time. It has for its object the production of a system for such multiple transmission wherein a proper balance of the circuits is maintained, ordinary signaling-currents cai1 .,be used without confusion of signals and without short-eircuiting, the static capacityof pieces of apparatus whose associated parts have a difference of potential is reduced or neutralized, and other important ends are attained, which will sufficienl-ly appear from the specification. Referring to the accompanying drawing, Figure 1 is a diagram of a system embodyin our invention as to its broad features,- and Fig. 2 is a similar diagram showing one coil with means to neutralize or compensate its static capacity. Fig. 3 shows one form of composite circuit. I

IriFig. l, X Y and X Y are subscribers" stations, connected, respectively, to the central stations S S. Between these central stations extend a pair of metallic trunk-lines 'l andfl", the former consisting of two wires "16 18 and the latter of two wires 17 19. These may be long-distance lines extending;

between distant points, or one may be a con tinuous circuit extending between distant.

points and the other may be composed of several shorter circuits connected up in tandein to form a return, as will be more fully pointed out hereafter, or both-may be built up circuits. At. station S the subscribers lines 2 4 and 6 8 terminate in spring-jacks J and J and these subscribers are served by 0 erators O and 0 whose respective "tele- I ones are'shown connected through their tening-keys K to the cord-circuits '10 12 and 14 16. The formercircuit has. terminal plugs P 1 and the latter (plugs P P. Rin'g- .mg-keys K are arrange and connected so rent from the generator G through the respective plugs r k to line.' All of this apparatus and these local circuits are of any usual or desired type, forming no distinctive! that. the operators can send alternating curr part of our invention. At the station S the subscribers lines '13 and 5 7 terminate in v jacks J and J and all the other parts are lettered to correspond to the similar parts at station S, being distinguished by ex onents of odd instead of even number. T system of numbering is uniformly adopted, all even numbers appertaining tostation S and the odd numbers to station S 'As shown in Fig.1, the trunltThas its conductors. 16 18 extending fromthe jack J" at station S to the jack J at station S; 1 '-Associated with the first-named jack is a-droja annunciator s, 'connectedso as to be cutout in thejack, when a lug isinserted; *Associated with the jack 7. is a similar annunciator a, similarly connected. The trunk T,

7.5 'at station S, is shown as similar to'the, trunk extending from jackJ at station S to jackJ T, its terminal jacks being'providedwvith- 'dro -annunciators'l' s? and s, respcctively.. 'Bot these trunks are. supposed to be pro erly transposed. at suitable mtervalsthroug out their lengths in the usual way, sothat 1.-

each individually will bcir'e'e from disturbances.

Accord to our inventlon we combine the .two" trunk-lines, heretofore-described, to

particularly in these days of universal adop tion of varying currents, it: must be a parent that the'difiicultiy in maintaining a p antom circuit compose in the manner wegne'n'tion,

free from noise, is much increased. Accord ing to our present invention, however, we'find I In addition, the trvo trunks are relatively and, jointly transposed,- treating each as a unitary conductor, for a purpose which will-now appear. 1

ility of, cross-talk, but to balance" thelines' 4 9 it possible not only" to thoroughlyisolate our. phantom circuit so thatf'there is no 'possi-f 'Q i I 845,796

' cuits are equally quiet, all signals are similarly received, and neither subscribers nor operators can'possrbly detect any difference between the real and the phantom circuits,

conductors 16 and 18 ot the trunk T, carry them oppositely through the double-wound 2o impedancecoil Cf, and unite thern as. one to the SleeveFcOntact'of the'same. jackJ At st.ationS- we take off taps= and 27; from the conductors 16 and 18 and carry them throughthe coil C to the spring-contact of 2 5 the jack J and similarly take off taps 21=and I 23 13pm conductors l7 and 19, carrying them ."through thecoilC" to. the sleeve of t s The jack J is providedwithgan annunci ator s,,-the same as, those of f the trunk jacks 3o J-and-J. The jack J has associatedwith it a similar an'nunciator. 8 These 'annuncia floors ,are all bridged across, their. respective clrcuitswhen the lines are idle, but are cut 'out whenithe 'lines are busy, either'the I 3 5 jacks or by suitable relays, It .will be under:

stood that the annunclators and their, conneetioris, aswell as the coils'and other pieces of apparatus, are all shown in the drawmgin sym olic -orconventional formstonlyg As our invention doeshot reside in or depend,

upon any particular type ofap aratus, we

have cont ted ourselves with 11 ustrating 'it- I in the simp est nianner possible. I The trunks an v 5 of us "as 'e ha e shown them,:for' talking "and signal both ways without regard .to 1 thelength r character of the circuits cQfl-j ne'c'ted wit them at their-terminals, On the otherha 'd, the trunkT, which isa'phantom circuit, I

ciency'noto ly upon the proper equalization and transpo ition of its componentcircuits T and T b t also upon the severance from the. hantom circuit in its operation of the subsidiary c nnected circuits, which of course may of variable length and possessed ofd imilar characteristics. This severance we my, laccomplish in several ways, two of hich are illustrated. One' is 6 by the introd ction of the coils C C C The other is by'the introduction'uof"arepeat ingcoil or COIlS R, this being resorted "to particularly when a trunk is employed in con 'neetion with su scribers lines deriving our- '6 5 rent from a cent alized battery;

- -c o'ntact of the jack "J Simi-' aflarly,we take off the taps 24 and 26 from thee can complete and susceptible "betweenthe coils mentioned.

pends for its balance and effi: In addition to the meansior'severing 1 x 5 I The coils C C, C and C are all alike, each comprising a subdivided core ofsoft iron, which may be suitably returned upon itself to form. a complete magnetic circuit, although shown 11'). simple. bar form. The windings are'double, of an equal number. of turns so disposed that their magnetic effects upon all parts of the core are the same. As indicated in' Fig. 1, these are twin wind- 5 ings, the conductors being laid on together throughout their length. In ractice it is preferable, however, to make w at are called layer windings-that is, to wind one layer of one conductor, insulate the layer with paper or otherwise, then wind 'a'second layer with the secondficonductor, insulate that and again wind alayer of the first conductor,

and soon. The insulationresist'ance of the coil .made in this flway is jvery much higher thanin the case ofaJ ;win-woundgcoil. .111

the latter. the insulation between ,the two:

conductors-is simply their individualinsulation, at any point in which apunctur e-pr breakdown isfatal to the entire coil, whereasin 'a layer jcoil the insulation between the sidespf'vthe line is due to the interposed layeredresistance.- p i For currents passing through either trunk T orT individually as a. met a l lic circuit that is,'in opposite direction through its com 9 5 po'nent wires-rthere is fsubstant ially no re tardation' due to the coils, aslthe double wind- 'ings neutralize each}, other in their magnetic efi'ects onatheincores. YMoreove'r' :we make the ,ohmic resistanceof the. coils as w-astposs re 0 sible'by using conductors of'large size; f

For currents passing over the trunk-lines T or-T, each'as a single conductor-that is,

over the component wire of each trunk in' arallelthe'coils{C,"C",-YC',andC oifer'sufcie'nt retardation -toprevent the passa e of any 'but direct or verylow frequencya ternating ourrents. .For voice-currents, therefore, and forall other currents of a reasonably high frequency. sent over the phantom circuit l 1 0 that circuit is limited 'b'oth'as to its; dis: chargerof function and astp its liab l ty to disturbance, to those portions of the, trunks circuitmg the "js aid. Such means corn rise the'co'ils C, C-,-C',and G, and the 'M'i; "Each of these-coils ls wo und ivlth'equal ahd oppositewindingafpreferablfput on in" Qlay'ers, of low ohmic resistane, but having'a I25 "considerable Jnumberofturns, as in the case, of the other'coila The function of'tlies'e lat-g ter coils is exactly-the reverse ofthat o f'the first iainedor trunk 'coila; E'ach co l, as 031 has its two: windings connected" together at; 13

and over the phantom extension-wires 1n 5 parallel will encounter no retardation etl'cct,

because the equal and opposite windings neutralize each other in their magnetic effect on the core. For currents passing over the two conductors of a trunk in opposite directions,

[ however; the phantom coil C C 0, or C offers considerable impedance, sufficient to lfar'the passage of alternating currentsof reasonable frequency.

The condensers M,'&c., are inserted in the i 5 branches to 27 in order to confine signaling- ,currents of low frequency or continuous in "character to the respective plugcircuits over which they are sent, thus also ]')I8\ enting short-circuiting We have ound the use 20 of these condensers to be essential, and we consider it an important part of our invention, because the coils C to 0 are of low ohmic resistanee,.ar.d 'tl'ierefore the branches 20 22, &e., wouldotherwise seriously interfere with signaling over-the trunks. We makelthese condensers each with a capacity referably not exceeding.two-microfarads.

t will. be observed that in-each branch cur rent "passing through the branch from one 0 side 'of 5 trunk to the other would have to -pass two condensers in series, which, by the rule governing capacities, would reduce the capacity of the branch to such an extentasto otl'er a very high apparent resistance to low- 3 5 frequency currents.

circuit would find in each sidethereof two condensers in parallel, giving ample capacity; The ultimate development of this idea is'of 40 course to so apportion the constants of the respective circuits that, while the phantomcircuitmight be a proximately resonantfor ringing currents o a given frequency, the ser1es connect1on of the condensers 1n the .451 branches 20 22, &c., would present a maximum resistance to ringing current over the trunks. In practice, however, we find that v fine adjustments are unncc essary, the margin between theseries and the parallel arrange- -5o ment of capacities being wide enough so long as each capacity is not too high.

While we have shown our )hant-om circuit T composed of the interme iate portio'ns of two contiliuoustrunks T and T, we have 'stated that pn'e or both of these trunks may be built up of shorter circuits. Such an ar- .-rangement'=is shown in Fig.- 3. Here the Y station's X and X are connected by metallic circuit, while stations Y and 1" are 6o similarly connected by a similar metallic circ uit These twocircuits have their respective conductors joined through the two \lVllld ings of a coil O similar inall res ects to the coil C. Here the two circuits and T" aic separated by the coil for currents in series I At the same time similar si naling-currents sent over the phantom througheach; but for currentsin arallel through the two sides of each circuitt ey are continuous and may form one side of a phantom circuit T 3, whose terminal branches are taken off. through coils C and C", as here- '0 tofore described. Inall such cases .we find that the static capacity of the linesis increased by the inclusion of. these coils ,for obvious reasons, Even in the pa'rrangernent shown in Fig. 1 the lumped capacity of each coil, being atone point in-the line, is undesirable We therefore providemeans for de creasing the'capacity of each coil or intro; duce a compensating self-inductance, which ably is separate, e;believe that the ldea of reducing or compensating this localized 'or lumped. capacity. and. the attainment of original with us, and We shall present the same broadly herein. I

Fig. 2 shows a :diagraphie develo mentof the coil 0, with its equal ,andsimi arly-dis posed windings. 'Webre ak' these windings,

preferably at their middle point, to secure a 0 good balance andinterposebetweelfrthe dissevered ends a'coil possessing self-inductance. One of these rcoils-is shownfatc in Eig, 2 with an adjustable core c. which maybe partly or wholly withdrawn to regulat' I iron in the core, and there 7 :the 'seI-f-inducti ance of the 'eircuitq Anether'fonn of coil'isi shown introduced inflthimiddl of theother winding of thernain 0011.01 lnthis jas'e'i plug-and-socket switc Wlth several 1 cc p ug's, is usedtocu in n olu'ttnior rgless turns in the coil c? I particular form .of ffco' pensat there are many forms;

hat-can; beg-adil t d I for-our purpose. *We al's'o findit quite possi- V ble' to design a compensating coilwithout adjustments. All such variations are included in our invention. 1

. I-n' connectingup ojnmon-battery lines the coils C, &c'.,can befdispensed with, as we I have stated. e haveishownfin Fig. 11 a repeat-ing-coilR, whosersecondaryds connectedto the conductors-16.118 andwhose primary goes to the jack J A condenser m is interposed to prevent magnetization .of the core and lowering of the eiiiciency of the coil R. VVitli this branch and its jack a pair of plugs P P are employed, and.theoperation sthe same as before describe We do not consider it necessary to give a detailedstatement of operation of our systern in general, as this is apparent from the description: The results We have attained are"co nmercial, and, as we believe we are the. first to commercially perfect land make avail-" table a system ofthis character, we feel entitled to all e uix/alents that may be found for w the specific orm s we here present.

A feature of ourinvention which we bee-'3; r

may be made as a art of the coil, but prefer 8 I greatly-improved transmission thereby is thegamountiof 5 o parallel and in part of a separate return-conno ayall, for the reason t at this particular condition has apparently never arisen before.

5 original with us, and it is the first successful said branch serially, substsfitially as. de- 'l for arbitrarilyv determining thecocilicicnt f self-induction of said auxiliary, cod at 111,.

- idea is, to prevent the low-frequencv ringing Condenseis in the regular circuit-that is,

' mercial'methods to make them perfectly uniform. Hence there is apt to be, due to the tamed:

ing circuit with condensers and including in found of considerable ractical importance, being, in fact, essentia, if absolutely uiet lines are desired, is the arrangement 0 the ringing circuit to'avoid cross-ringing. The

current overone line from affecting the other.

the talking-circuitas at M M M M, &e., are necessarily not exactly equal capacity, it being almost impossible by ordinary comlow frequency, a tendency to crossring from one line to the other, or, in other words,ringing in one line can be heard in the receivers of the other line. In attacking this problem the expedients of ordinar' practice were of It has been proposed to use bridge-coils without condensers and to use bridged condensers without coils, (this arrangement, however, being ino erative, as it creates a short circuit for big -frequency voice-currents,) but'so far as we knowthe combination we have arranged and which is herein set forth is commercial arrangement that has been at- We have found that by bridging the ring each side thereof a retardation-coil of a contirely; and, in fact in many cases we do abhe last trace of cross dis- We ascribe this ported to the current, the curve representing the alternations being smoothed ofiand ap proximatin a sine curve. Hating t us described our invention, what we claim is-- 1. In a system i" or the transmission of electrical currents having different characteris tics, a wire-circuit composed of two conductors adapted to convey current through its com onent conductors seria'lly,.and a second or an'tom circuit com osed in part of said first-named circuit with its conductors in duc'tor, ccnnected to both conductors of the first circuit by a branch wire bridged across the same, together with an electromagnetic coil and a condenser included in said branch and so connected as to impede the passage of,

either alternating or direct currents through tricul currents having different characterisg tics, a metallic circuit adapted to transmit currents over its conductors serially, and a 1 the passageof either direct or alternating current-through said branch from one side of the metallic circuit to the other is impeded, substantially as described. Y

3. In a duplex system of transmission, the I combination of the following instrumentalities: two metallic ell-wire. circuits, each adapted for transmission over its own constituent conductors in series, bridges across each of the metallic circuits, each bridge conta' v a double difierentially-wound coil, a

pair 0 condensers in each bridge, one on each side of the coil, connections between the mid- "dle points of the windings of the corresponding coils appertaining to the two metallic circuits, and means to include, talking or signal.- ing apparatus in said connection, wherebym addition to the two metallic circuits a third or phantom circuit is produced, subStan v tially as described;

A. Ina telephonesystem, two metallic circuits as 'I. and T,-each terminatinggin a connective device, bridges across each ofsa d c rs cuits, a double and differentially-wound coil,

in-each: bridge, connections from the middle points of each corresponding-pair of boils, as,

C and C", to a third connective device, a pair of condensers in each bridge, one on each side of each coil, and means to bring talking and signaling apparatus into 0 erative connection with-said connective evices, substantially as described. r 5.;In a telephone system, line-circuits, double-wound coils having their respective windings included in said circuits, and means interpolated in the windingsof each coil .to increase the self-inductance of the ,coil and the circuit, substantially as described. I

6. In a telephone system, a metall c circuit, 'a differential or neutral'coil, having its windings included therein, together with an auxiliary coil possessing considerable self-1nductance connected to the first or neutral .115

coil, substantially as described.

'7. In a telephone system, a metallic circuit, a differential or neutml coil haying its windings included therein. an auxiliary coil possessing considerable self-inductance connected to the first or neutral coil, and means substantially as described.

8. In a duplex telephone system, two cir cuits, a bridge across each' circuit, condensers in said bridges, wringing circuit, means for second or phantom circuit composed in part 1 connecting the same to the first-named circuits, and, means in said ringing circuit to i smooth down or modify the character of the l possessing considerable selfdnductance con i nected to the first or neutral coil, and means to determine the number of active turns in said auxiliary coil, substantially as described.

In testimony whereof We have hereunto set our hands, this 19th day of February, A. D. 1904, in the presence of two subscribing \vitnesses.

JACOB W. LATTIG. CHARLES LANE GOODRUM.

Witnesses:

MARY O. MCCARTHY, E' R. CONNELLY. 

